In the case of those fibre spinning plants, the endless multi-fibre yarn, which is supplied continuously, has to be laid continuously into cans after leaving the textile finish device connected in series with the spinning section and the take-up device. This means intermediate storage of fibre yarn, since in a subsequent procedure, the fibre yarns have to be extracted from several cans simultaneously and treated jointly. This procedure requires that the fibre yarn is laid accurately into the cans, i.e. it has to be laid uniformly and distributed evenly over the cross section so that there will be no cavities and at a later stage the yarn can be withdrawn from the filled can without knotting. To fulfill this requirement, the operating sequence must not be disturbed during can changing. However, it is also important that all cans contain the same quantity of fibre yarns, as otherwise it would result in wastage of yarns when joining the yarns from several cans.
Because cans are to be exchanged beneath the yarn which falls continuously like a water jet, the transfer of the yarn from the filled can into the empty can must take place as quickly as possible in order to prevent unnecessary waste due to yarn being dropped by the side of the can.
For this reason, repeated attempts have been made to carry out the changing of cans without intervention of the operating personnel, i.e. automatically, because this would best meet the above demands.
There are various kinds of yarn laying devices for fibre spinning. There are systems in which the can remains stationary, while the yarn is laid by yarn guide, which is controlled correspondingly, and systems in which the yarn guide remains stationary and the can performs corresponding motions. There are also systems which are a combination of the above named types, with corresponding variations. As soon as a can is filled on the yarn laying platform, it has to be exchanged for an empty one.
Because, at present, there is a tendency to use larger cans or drums for laying fibre yarns, and it is difficult for the operating personnel to lift the heavy cans, they are transported on roller conveyors or equipped with rollers. The can which is to be filled must always be placed accurately on the fixed or movable platform, or the rotary table. In the case of the usual yarn laying devices, it has proved difficult to combine the changing procedure into one working process and furthermore to make this into an automatic operation. There are automatic can changing devices, but they have not yet produced any solution which is generally satisfactory. They are either very expensive and require too much additional space which is not usually available for new plants and which does not exist at all in plants already in operation, or too long an interval occurs between the changing of the cans, resulting in a loss of product. Therefore, purely manual changing of cans is still preferred to a large extent.